ngc 2937

The Porpoise Galaxy from Hubble

What’s happening to this spiral galaxy? Just a few hundred million years ago, NGC 2936, the upper of the two large galaxies shown, was likely a normal spiral galaxy – spinning, creating stars – and minding its own business. But then it got too close to the massive elliptical galaxy NGC 2937 below and took a dive.

Dubbed the Porpoise Galaxy for its iconic shape, NGC 2936 is not only being deflected but also being distorted by the close gravitational interaction. A burst of young blue stars forms the nose of the porpoise toward the right of the upper galaxy, while the center of the spiral appears as an eye. Alternatively, the galaxy pair, together known as Arp 142, look to some like a penguin protecting an egg. Either way, intricate dark dust lanes and bright blue star streams trail the troubled galaxy to the lower right.

In a billion years or so the two galaxies will likely merge into one larger galaxy.

Arp 142

This image shows the two galaxies interacting. NGC 2936, once a standard spiral galaxy, and NGC 2937, a smaller elliptical, bear a striking resemblance to a penguin guarding its egg. This image is a combination of visible and infrared light.

This galactic pair has nicknamed after both of them – the curve of a porpoise or a dolphin can be seen in the blue- and reddish shape towards the bottom of the frame, when paired with the glowing orb just beneath it, resemble a bird or penguin guarding an egg.

The form of the penguin itself is made up of a single galaxy that has been distorted and ripped apart. This galaxy, named NGC 2936, was once a normal spiral like the Milky Way, until it started interacting with its egg-like neighbour, an elliptical galaxy named NGC 2937. Together, these two galaxies make up a pair dubbed Arp 142.

The pair is pulling each other and interacting, slowly changing their appearances and disrupting their gas, dust and stars. In around a billion years these two might come together to form a single galaxy, and the merging process will be complete.

(NASA) The Porpoise Galaxy from Hubble Image Credit: NASA, ESA, and The Hubble Heritage Team (STSci/AURA)

What’s happening to this spiral galaxy? Just a few hundred million years ago, NGC 2936, the upper of the two large galaxies shown, was likely a normal spiral galaxy – spinning, creating stars – and minding its own business. But then it got too close to the massive elliptical galaxy NGC 2937 below and took a dive. Dubbed the Porpoise Galaxy for its iconic shape, NGC 2936 is not only being deflected but also being distorted by the close gravitational interaction. A burst of young blue stars forms the nose of the porpoise toward the left of the upper galaxy, while the center of the spiral appears as an eye. Alternatively, the galaxy pair, together known as Arp 142, look to some like a penguin protecting an egg. Either way, intricate dark dust lanes and bright blue star streams trail the troubled galaxy to the lower right. The above recently-released image showing Arp 142 in unprecedented detail was taken by the Hubble Space Telescope last year. Arp 142 lies about 300 million light years away toward the constellation, coincidently, of the Water Snake (Hydra). In a billion years or so the two galaxies will likely merge into one larger galaxy.

This image shows the two galaxies interacting. NGC 2936, once a standard spiral galaxy, and NGC 2937, a smaller elliptical, bear a striking resemblance to a penguin guarding its egg. This image is a combination of visible and infrared light, created from data gathered by the NASA/ESA Hubble Space Telescope Wide Field Planetary Camera 3 (WFC3).

This interacting galaxy duo is collectively called Arp 142. The pair contains the disturbed, star-forming spiral galaxy NGC 2936, along with its elliptical companion, NGC 2937 at lower left.

Once part of a flat, spiral disk, the orbits of the galaxy’s stars have become scrambled due to gravitational tidal interactions with the other galaxy. This warps the galaxy’s orderly spiral, and interstellar gas is strewn out into giant tails like stretched taffy.

Gas and dust drawn from the heart of NGC 2936 becomes compressed during the encounter, which in turn triggers star formation. These bluish knots are visible along the distorted arms that are closest to the companion elliptical. The reddish dust, once within the galaxy, has been thrown out of the galaxy’s plane and into dark veins that are silhouetted against the bright starlight from what is left of the nucleus and disk.

The companion elliptical, NGC 2937, is a puffball of stars with little gas or dust present. The stars contained within the galaxy are mostly old, as evidenced by their reddish color. There are no blue stars that would be evidence of recent star formation. While the orbits of this elliptical’s stars may be altered by the encounter, it’s not apparent that the gravitational pull by its neighboring galaxy is having much of an effect.

Above the pair, an unrelated, lone, bluish galaxy, inconsistently cataloged as UGC 5130, appears to be an elongated irregular or an edge-on spiral. Located 230 million light-years away, this galaxy is much closer to us than the colliding pair, and therefore is not interacting with them. It happens to lie along the same line of sight to foreground Milky Way stars caught in the image.

Arp 142 lies 326 million light-years away in the southern constellation Hydra. It is a member of the Arp catalog of peculiar galaxies observed by astronomer Halton C. Arp in the 1960s.